DE102018122917A1 - Device for the direct optical recording of skin prints - Google Patents

Abstract

The invention relates to a device for the optical direct recording of skin prints. The object of the invention is to find a new possibility for the optical direct recording of skin prints of human autopodiums, which allows a display layer for person identification according to the FBI standard directly below the contact surface (11) a light guide layer (141) is arranged below the sensor layer, which has at least one LED (142) on a narrow side and is provided with light decoupling structures (144) which, by means of the angle of inclination ε and differences in the refractive indices from neighboring layers, provide a directional light decoupling from the light guide layer (141) allow with a defined angle that leads to internal total reflection (TIR) on the contact surface (11) at the transition from the top layer (12) to air, and with a small divergence angle range of ≤ +/- 15 °, whereby between the top layer (12) and the sensor layer (13) and between Senso r layer (13) and light guide layer (141) first and second adhesion layers (15, 16) are present, the refractive indices of which are at least 1% and at most 30% smaller than the refractive indices of the light guide layer (141) and the sensor layer (13).

Description

The invention relates to a device for the optical direct recording of skin prints, in particular for recording papillary lines of multi-finger or hand prints.

On the one hand, the prior art knows systems which serve for the verification of biometric features, in which a match with stored features must exist, for example to enable access control for defined restricted areas.

Other systems are used for identification by comparison with comparison databases, for example passport and visa creation, personal identity determination at border controls, in particular at airports, or in the identification process by the police. The requirements regarding quality, resolution and fidelity of the recorded images of the skin prints are very extensive with the latter systems.

Not least due to the high demands of organizations entrusted with identification measures, such as the Federal Bureau of Investigation (FBI) of the United States, there is a high degree of standardization in these systems, on the one hand to ensure that the detection is as unambiguous as possible and on the other hand that data records are used different systems have been included to make them comparable.

A high-quality system design is required to meet these requirement criteria. In the case of an optical system, this means, for example, that not only the exposure sensor or sensors have to meet the requirements, but also the lighting and all other components necessary for image generation, especially when large areas of skin, i.e. more than one finger (for Example a complete hand), should be recorded at the same time.

Different systems are currently used to record fingerprints and handprints that meet the high quality requirements mentioned.

On the one hand, capacitive, semi-transparent TFT sensors are used, in which user guidance can be implemented using a display below the sensor. Reading security-related documents such as B. Passports, driving licenses, tickets, boarding cards etc. is not possible, so that a separate device or at least an additional optical sensor layer would be necessary, but this would drive up the device costs.

On the other hand, devices are entering the market that implement direct optical scanning of the skin prints, i.e. in which the object to be photographed (fingers, four fingers or hand) is placed on a support surface directly above the light-sensitive sensor array, without using optical imaging systems such as macroscopic lenses, prisms, imaging gratings, etc. These systems can also combine the recording of skin impressions with the advantages of a visual user guidance and an optical recording of documents on the same contact surface by using optical semi-transparent TFT sensors.

A system in which a display is positioned under the optical sensor is already out of the DE 10 2015 115 484 B3 known. There, the display also functions as lighting or is used as background lighting, so that the object lying on it is illuminated diffusely, that is to say in a non-directional manner. The light scattered back from the object is then detected by the light-sensitive elements of a sensor. The thickness of the cover layer between the support surface and the light-sensitive elements is limited to a few micrometers, since the resolution and contrast decrease rapidly with increasing distance between the sensor and the support surface.

Nevertheless, various solutions are known which enable or require a greater thickness of the cover layer with the same image quality.

For this purpose, the illuminating light of the backlight is collimated on the one hand, as in the case of various designs from the US 2018/0121701 A1 ( WO 2017/118030 A1 ) known. However, it proves disadvantageous that additional optical elements have to be integrated between the lighting and the support surface in order to achieve the desired light shaping. This additional layer increases the thickness of the entire device, is expensive and complex to manufacture.

Similarly, in the US 2018/0165497 A1 has been described to embed an optical image sensor in a flat panel display, which can contain a fingerprint sensor. The structure comprises a display screen with a display and a non-display area, a light guide, which lies with the same length and width on the display screen and consists of two cover plates connected with a low-refractive adhesive layer, the light being coupled in outside of the display layer of the flat screen, by one The light-refractive layer below the display layer is coupled into the lower cover plate at an angle between 70 ° and 75 ° and passed on in a totally reflected manner. A portion of this totally reflected light is coupled into the upper cover plate at a smaller angle at the refractive layer and reflected back towards the display as an internal total reflection (TIR - Total Internal Reflection) at the outer boundary layer, whereby it transmits through the low refractive layer and the lower cover plate can also pass without reflection. Since the display is an AMOLED (active matrix organic light-emitting diode), it can also be used as a sensor layer. This enables fingerprints and - using IR light - veins to be detected.

A disadvantage is the selective lateral coupling of the light via a diffraction grating, for which a laser source is required in order to couple the required light intensities into a light guide. As a result, the light is only illuminated in a triangular area. In addition, the light is extracted from the light guide via the usual scattering centers, such as in the US 2018/0128957 A1 described, as lighting for high-quality fingerprint recording that meets the FBI standards, limited by the fact that the proportion of illuminating rays for the TIR principle is rather insufficiently small.

The invention has for its object to find a new possibility for the optical direct recording of skin prints of human autopodia, which allows a display layer for user guidance directly below the support surface in the case of high requirements for person identification according to the FBI standard, without in particular the local resolution of the fingerprint images decreasing.

According to the invention, the object is achieved in a device for the optical direct recording of skin impressions, with a laminate which contains a support surface which is formed by a cover layer of the laminate, as well as a sensor layer and a light source unit, the sensor layer being arranged in a sensor grid, light-sensitive elements and transparent areas has been achieved in that the light source unit is designed as a light guide layer and is arranged below the sensor layer, the light guide layer on a narrow side having light coupling by means of LEDs, that the light guide layer is provided with light decoupling structures which are based on an inclination angle of the light decoupling structures and on the basis of differences of the refractive indices between the neighboring layers of the light guide layer up to the cover layer, a directional light coupling out of the light guide layer at a defined angle, which after passing through of all layers up to the top layer on the contact surface at the transition to air leads to internal total reflection (TIR), as well as with a small divergence angle range of ≤ +/- 15 °, in order to achieve a high local resolution of the skin print to be recorded, that between top layer and sensor layer a first adhesion layer and a second adhesion layer are present between the sensor layer and the light guide layer, the second adhesion layer having a refractive index which is at least 1% and at most 30% smaller than the refractive indices of the light guide layer and the sensor layer, whose refractive indices are between 1.45 and 1, 8, and the first adhesive layer has a refractive index that is at least as large as that of the second adhesive layer.

The LED light coupling advantageously has a precollimation optics arranged downstream of the LED on the narrow side of the light guide layer, with which a horizontal divergence between 2.5 ° and 30 ° is set in the beam bundle coupled into the light guide layer in order to improve the resolution of the skin impression to be recorded to reach.

The pre-collimation optics are expediently a refractive optical element which is arranged on the narrow side of the light guide layer and is preferably incorporated in the form of a convex or GRIN lens on the narrow side of the light guide layer. In another preferred embodiment, the pre-collimation optics within the light guide layer are designed in the form of a concave lens made of a medium with a lower refractive index than the light guide layer.

A plurality of closely adjacent LEDs is expediently arranged along a narrow side of the light guide layer, so that their beam bundles bring about an adjusted light intensity in the light guide layer due to the horizontal divergence after a defined coupling-in length.

It has also proven to be advantageous for the light coupling in that a corner light coupling with at least one LED is arranged on at least one narrow side provided by shortening a corner of the light guide layer, with a decrease in the intensity of the divergent beam bundle coupled into the light guide layer due to a growing fill factor of size and density Light decoupling structures is compensated. A diffusing screen is expediently arranged between the LED and the narrow side of the shortened corner of the light guide layer for uniform distribution of the coupled light in all solid angles, so that no light drop on the shortened corner of adjacent narrow sides of the light guide layer has to be compensated for.

It also proves to be advantageous that the refractive index of the first adhesive layer is as large as the refractive index of the second adhesive layer, so that a proportion of stray light that emerges from the skin areas lying on the support surface as a result of excitation generated by ambient light is due to TIR inside the cover layer is hidden from spreading in the direction of the sensor layer.

The laminate preferably has a display for displaying user information, which is applied below the light guide, the display being an LCD, OLED, QLED etc. The display can be attached to the underside of the light guide layer either detachably without an adhesive layer or by means of another low-index adhesive layer with a refractive index that is at most as large as that of the second adhesive layer, so that scattered light or light reflected on the back of the sensor layer absorbs from the display can be. As a result, the light guide layer is more independent of the reflection component of the sensor layer and can always have the same light output structures. Furthermore, the laminated body becomes mechanically more stable through the gluing of the massive display.

In addition, the display can be used as an additional luminescent layer for illuminating documents in order to provide light for document illumination in addition to the illumination of the light guide layer provided by residual divergence from the TIR angular range.

The light coupling expediently contains a plurality of LEDs densely packed with a center distance between 1 mm and 10 mm, which are pre-collimated in such a way defined that after a coupling-in length of at least 2 mm, the LEDs have overlapping light radiation cones in order to produce a homogeneous illumination. The center distance of the LEDs is preferably 3-6 mm with preferably a half-width (FWHM) of the radiation of 10 ° or a divergence of genz +/- 5 °, the coupling length preferably being 2-20 mm.

In a special embodiment of the invention, the light decoupling structures are advantageously designed in such a way that only between 50% and 95% of the illuminating light decoupled from the light guide layer are totally reflected light components on the contact surface in the cover layer while transitioning to air, while a remaining remaining light component for illuminating documents is usable.

The light guide layer expediently has a fill factor of the light outcoupling structures, formed by the size and spacing of the light outcoupling structures, which is at least so large for each point of the light guide layer that the light outcoupling structures are not visible in an imprint image of skin areas to be recorded. The light outcoupling structures are preferably at a distance s which is very much smaller than a resulting beam divergence of the light outcoupling structures of the light guide layer. Furthermore, the light guide layer has a high transparency, so that the haze is less than 20%.

In a further advantageous embodiment, a further transparent light guide layer is attached under the transparent light guide layer and connected to it by a further adhesion layer which has a low refractive index like the first and second adhesion layers.

In this case, a first variant proves to be expedient, in which the light guide layer and the further light guide layer have the light coupling on opposite narrow sides of the layer body in order to fall back on the further light guide layer if the image of a skin area recorded with the primary light guide layer is of poor quality (defect columns, pixels , wet finger, dry finger, ...), for which a second image recorded with the further light guide layer, which is shifted to the first image, can be used individually or fused with the first image (taking into account an existing offset).

In a second advantageous variant, the light guide layer and the further light guide layer can have the light coupling in on the same narrow side of the layer body and have light decoupling structures with the same orientation, the light guide layer and the further light guide layer having light decoupling structures with such different inclination angles ε can have, as far as these different inclination angles ε each lighting angle β generate that lead to total reflection on the contact surface. This is interesting for the efficiency of the system if both light guide layers are operated quasi-parallel and the light is coupled out at different points, which enables higher light intensities to illuminate the skin area on top. Additional light guide layers with corresponding LED arrays z. B. for lighting certain limited areas can also be advantageously implemented, z. B. to illuminate the document and fingers at the same time.

The invention is based on the basic idea that when the functions of fingerprint recording and document recording are combined in one device, which is also intended to implement display functions for user guidance in the support surface, the light intensity of the skin prints generally becomes insufficient or the resolution and contrast of the images no longer meet the required FBI standard. The invention solves these problems in that a light guide layer is arranged below a semitransparent sensor layer and the light is coupled in by means of LEDs on a narrow side of the light guide layer, the light guide layer being provided with light decoupling structures which are based on the angle of inclination of the light decoupling structures and the refractive index differences between the adjacent layers of the light guide layer up to the top layer, directional light decoupling at a defined angle, which leads to a small divergence angle range of ≤ +/- 15 ° on the contact surface at the transition to air to TIR in order to achieve a high local resolution of the skin impression to be taken. The decoupling of light can be further improved in a targeted manner by means of refractive indices of the adhesive layers and neighboring layers that are adapted to the light guide layer.

With the invention, it is possible to record skin imprints of human autopodia by means of an optical direct scanner with high quality according to FBI standards and also to display information on user guidance by means of a display below the contact surface and the sensor surface, without this leading to a deterioration in the local resolution of the skin imprint images.

• 1: eine prinzipielle Ausführung der erfindungsgemäßen Vorrichtung mit einem Schichtkörper, enthaltend eine Deckschicht mit Auflagefläche für aufzunehmende Objekte, eine Sensorschicht und eine Lichtleiterschicht als Lichtquelle,
• 2: eine vorteilhafte Ausführung der Erfindung mit einem Display zur Nutzerführung, das unterhalb des in 1 gezeigten Aufbaus angeordnet ist, wobei über den Sensorelementen eine zusätzliche Blendenschicht zur Verminderung des Lichteinfalls von mehreren Querorten auf ein und dasselbe Sensorelement vorhanden ist,
• 3a: einen Ausschnitt des Schichtkörpers mit speziellen Lichtauskoppelstrukturen an der Unterseite der Lichtleiterschicht zur Auskopplung von Strahlenbündeln, die die Auflagefläche unter einem Totalreflexionswinkel erreichen,
• 3b: einen Ausschnitt des Schichtkörpers mit speziellen Lichtauskoppelstrukturen an der Oberseite der Lichtleiterschicht zur Auskopplung von Strahlenbündeln, die die Auflagefläche unter einem Totalreflexionswinkel erreichen,
• 3c: zwei Abschnitte der Lichtleiterschicht mit unterschiedlich geformten Lichtauskoppelstrukturen der Lichtleiterschicht von 3b in einer Draufsicht, bei der die Lichtauskoppelstrukturen in Richtung des Lichteinfalls ansteigende Vierecksflächen, wie z. B. Trapeze, Rechtecke, sind,
• 4a: einen Ausschnitt des Schichtkörpers gemäß der Ausführung von 3a mit einer vergrößerten keilförmigen Lichtauskoppelstruktur und Darstellung eines repräsentativen Strahlenverlaufs, der an der Lichtauskoppelstruktur zur Auflagefläche hin ausgekoppelt wird und letztere unter einem Totalreflexionswinkel erreicht,
• 4b: eine zu 4a erstellte Darstellung des Lichtleitwinkels des in der Lichtleiterschicht geführten Lichts über dem Neigungswinkel der keilförmigen Struktur, um die Abhängigkeit des Strahlverlaufs durch die Grenzflächen des Schichtkörpers aufgrund unterschiedlichen Brechungsverhaltens als Zustandsdiagramm aufzuzeigen,
• 5: einen Ausschnitt des Schichtkörpers gemäß 1 mit aufgelegtem Finger unter Einwirkung von Umgebungslicht (Sonne), das bei dieser Ausführung innerhalb der Deckschicht durch Totalreflexion von den Sensorelementen der Sensorschicht ferngehalten, d.h. ausgeblendet wird,
• 6: eine besondere Ausführungsform der erfindungsgemäßen Vorrichtung, bei der unterhalb der Sensorschicht zwei Lichtleiterschichten unmittelbar übereinander und oberhalb eines darunter angeordneten Displays vorhanden sind,
• 7: eine weitere vorteilhafte Ausführungsform der Erfindung, die eine zusätzliche Spektralfilterschicht über der Sensorschicht und eine zusätzliche Substratschicht zwischen Sensorschicht und Lichtleiterschicht aufweist,
• 8: eine besonders vorteilhafte Ausführungsform der Erfindung, bei der infolge von Lichtauskoppelstrukturen mit angepassten Neigungswinkeln für TIR-Aufnahmen von Hautabdrücken und angepassten Neigungswinkeln zur Aufnahme von Dokumenten möglich ist, 9: mehrere vorteilhafte Ausführungsformen der Lichteinkopplung in die Lichtleiterschicht der erfindungsgemäßen Vorrichtung, bei denen an einer Schmalseite der Lichtleiterschicht (a) unkollimierte LEDs eingekoppel sind, wobei jeder Objektpunkt mehrere Bildpunkte erzeugt, (b) herstellerseitig vorkollimierte LEDs unmittelbar einstrahlen, (c) LEDs mit einer zwischengeordneten Vorkollimationsoptik einkoppeln, (d) LEDs über in der Lichtleiterschicht eingebettete Vorkollimationsoptiken einstrahlen und (e) LEDs unterschiedlicher Wellenlängen zur alternativen spektralen Beleuchtung abwechselnd angeordnet sind,
• 10: eine Darstellung von dicht gepackten, vorkollimiert eingekoppelten LEDs zur Erläuterung der erreichbaren Beleuchtungshomogenität in Abhängigkeit von Mittenabstand der LEDs und Einkoppellängen der Strahlenbündel,
• 11: mehrere vorteilhafte Ausführungsformen der Lichteinkopplung in die Lichtleiterschicht der erfindungsgemäßen Vorrichtung, bei denen an einer eingekürzten Ecke der Lichtleiterschicht eine Eckenbeleuchtung (a) mit einer unkollimierten LED realisiert ist, wobei jeder Objektpunkt (in horizontaler Richtung) genau einen Bildpunkt erzeugt, (b) zwei LEDs mit dazwischen angeordneter Streuscheibe und (c) mit einer unkollimierten LED, wobei die eingekürzte Ecke der Lichtleiterschicht eine angepasst gekrümmte Einkopplungsfläche aufweist.

The invention will be explained in more detail below using exemplary embodiments. The drawings show:

• 1 a basic embodiment of the device according to the invention with a laminated body, comprising a cover layer with a supporting surface for objects to be recorded, a sensor layer and a light guide layer as light source,
• 2nd : an advantageous embodiment of the invention with a display for user guidance, which is below the in 1 The structure shown is arranged, with an additional diaphragm layer above the sensor elements to reduce the incidence of light from several transverse locations on one and the same sensor element,
• 3a a section of the laminated body with special light coupling structures on the underside of the light guide layer for coupling out beams that reach the contact surface at a total reflection angle,
• 3b : a section of the laminate with special light coupling structures on the top of the light guide layer for coupling out beams that reach the contact surface at a total reflection angle,
• 3c : two sections of the light guide layer with differently shaped light coupling structures of the light guide layer from 3b in a plan view, in which the light decoupling structures rising in the direction of light incidence quadrangular surfaces, such as. B. trapezoids, rectangles,
• 4a : a section of the laminate according to the execution of 3a with an enlarged wedge-shaped light decoupling structure and representation of a representative beam path, which is decoupled at the light decoupling structure towards the support surface and reaches the latter at a total reflection angle,
• 4b : one too 4a created representation of the light guide angle of the light guided in the light guide layer over the angle of inclination of the wedge-shaped structure in order to show the dependence of the beam path through the interfaces of the layer body due to different refractive behavior as a state diagram,
• 5 : a section of the laminate according to 1 with the finger placed on it under the influence of ambient light (sun), which in this embodiment is kept away from the sensor elements of the sensor layer by total reflection within the cover layer, ie is hidden,
• 6 a special embodiment of the device according to the invention, in which there are two light guide layers directly above one another and above a display arranged underneath the sensor layer,
• 7 a further advantageous embodiment of the invention, which has an additional spectral filter layer over the sensor layer and an additional substrate layer between the sensor layer and the light guide layer,
• 8th a particularly advantageous embodiment of the invention, in which, as a result of light decoupling structures with adapted inclination angles for TIR images of skin prints and adapted inclination angles for accommodating documents, it is possible, 9 : Several advantageous embodiments of the light coupling into the light guide layer of the device according to the invention, in which (a) uncollimated LEDs are coupled in on a narrow side of the light guide layer, each object point producing several pixels, (b) LEDs pre-collimated by the manufacturer, (c) LEDs with one Coupling intermediate precollimation optics, (d) illuminating LEDs via precollimation optics embedded in the light guide layer and (e) LEDs different wavelengths are alternately arranged for alternative spectral illumination,
• 10th : a representation of tightly packed, pre-collimated coupled LEDs to explain the achievable lighting homogeneity depending on the center distance of the LEDs and the coupling lengths of the beams,
• 11 : Several advantageous embodiments of the coupling of light into the light guide layer of the device according to the invention, in which corner lighting (a) is realized with an uncollimated LED at a shortened corner of the light guide layer, each object point (in the horizontal direction) producing exactly one pixel, (b) two LEDs with a diffusing screen arranged between them and (c) with an uncollimated LED, the shortened corner of the light guide layer having an adapted curved coupling surface.

The device according to the invention comprises in a basic structure - as in 1 shown - a laminate 1 starting from a support surface 11 for the objects to be recorded (fingers 2nd or document 3rd , not shown) a top layer 12th whose outer surface is the contact surface 11 provides a sensor layer 13 with light-sensitive sensor elements 131 , which has a defined partial transparency for the light of the underlying light source unit 14 that in the form of a light guide layer 141 is formed and on one or more LEDs on at least one narrow side 142 has as light sources, which are provided for coupling in more or less well pre-collimated light. Between the top layer 12th of the laminate 1 and the sensor layer 13 is an adhesive layer in the form of a first adhesive layer 15 and between the sensor layer 13 and light guide layer 141 is a second layer of adhesion 16 introduced as an adhesive layer. The second adhesive layer has 16 a refractive index that is at least 1% and at most 30% smaller than the refractive indices of the light guide layer 141 and the sensor layer 13 with a refractive index between 1.45 and 1.8, and the first adhesive layer 15 has a refractive index that is at least as large as that of the second adhesive layer 16 .

That of the (n) LED 142 radiated light is due to the light guide properties of the light guide layer 141 at a light guiding angle α forwarded. Because of the light decoupling structures explained in detail below 144 the light guide layer 141 are portions of the in the light guide layer 141 with the light guide angle α propagating light at a defined angle so that after passing through all layers of the laminate 1 to the top layer 12th on the contact surface 11 an angle of illumination at the transition to air β is set for internal total reflection (TIR), the light decoupling structures 141 allow decoupling of light beams with a small divergence angle range of ≤ +/- 15 ° in order to achieve a high local resolution of the skin impression to be recorded.

It should be mentioned at this point that the refractive indices defined above are slightly different from that of the light guide layer 141 should deviate, lose their meaning if and only if the thickness of the adhesive layers approaches the order of magnitude of the light wavelength used. In that particular case, the light does not perceive the adhesive layers and the refractive indices of the subsequent layers apply, which define the refraction of light or total reflection.

In 2nd is one opposite 1 extended version of the device shown below the light guide layer 141 a display 17th having. the display 17th can on the light guide layer 141 either detachably (without adhesive layer) clamped, clamped in or attached in some other similar way. However, is shown in 2nd a version with another adhesive layer 18th that one with the second adhesive layer 16 comparably low refractive index and which the display 17th with the light guide layer 141 permanently glued.

The adhesive layers 15 , 16 , 18th are for at least portions of illuminating light from the light guide layer 141 and an optional one under the light guide layer 141 adjacent displays 17th transparent. This can be an optically transparent double-sided adhesive tape (OCA) or a liquid adhesive that has been cured, for example, using heat or UV radiation (LOCA). These adhesives can be, for example, silicones, acrylate, epoxies.

As a light guide layer 141 polycarbonate (PC), polymethyl methacrylate (PMMA), glass or other optically transparent materials with a refractive index n ~ 1.5 are used. However, other materials with a refractive index between 1.45 and 2.0 can also be used as the light guide layer 141 are used. The light-guiding effect at the points of the light-guiding layer 141 without light decoupling structures 144 is determined by the difference in the refractive indices between the light guide layer 141 as well as second and further adhesive layers 16 , 18th realized.

The sensor layer 13 has photosensitive elements arranged in a grid 131 With a resolution of 100 ppi to 1000 ppi and, depending on the light intensity detected, passes on electronic signals that are converted into a gray value image. The photosensitive elements 131 the sensor layer 13 are photodiodes with a defined sensitivity for a certain spectral range of light. In a preferred embodiment, the sensitivity of the photosensitive elements 131 on the emitted illuminating light of the light guide layer 141 spectrally adjusted to increase the signal-to-noise ratio (SNR).

It should be noted that all of the above information regarding the materials and parameters of the adhesive layers 15 , 16 and 18th , the light guide layer 141 and the sensor layer 13 also apply to all other arrangements described.

As a result of the partial transparency of the sensor layer 13 , in which the transparency is advantageously achieved in that each sensor element 131 within the regular pixel grid of the sensor layer 13 a transparent area 132 includes instructions or other user information with sufficient intensity on the support surface 11 the top layer 12th can be seen by the user of the device.

Through the entire sensor layer 13 evenly existing defined fill factor of non-transparent sensor elements 131 and transparent areas 132 can display the information 17th can also be displayed without distortion, cloudiness or color restrictions.

The resolution of a recorded skin print 21 to improve and also the influence of stray light 4th (only in 5 shown) that from ambient light or the internal light of the display 17th in the preferred embodiment of 2nd over the photosensitive elements 131 the sensor layer 13 an aperture layer 133 to limit the detectable angular range of each photosensitive element 131 arranged. In this way, the influence of horizontal and vertical divergence of the illuminating light is reduced and, as a result, thicker cover layers can be created 12th or additional substrate layers 172 use with constant resolution, for example protection and / or stability of the laminate 1 and improve the entire device.

In order to effectively block stray light or lighting angles that should not be detected, non-transparent aperture materials are necessary. Are preferred for the individual diaphragms in the diaphragm layer 133 Materials that are used in photolithographic coating processes due to their good structurability, for example metals such as chromium, aluminum, gold, molybdenum, copper, silver, silicon. However, due to the reflective properties of these materials, undesirable reflections can occur on the surfaces of the diaphragms, which restrict the contrast of the image recording, increase noise or generate double images. Therefore, absorbent organic materials such as. B. polytetrafluoroethylene, and absorbent inorganic materials, such as diamond-like carbon layers, black chrome, copper indium disulfide, or materials with a special microstructure. Particularly preferred are materials that can be printed, e.g. B. by screen printing, as a structured diaphragm layer 133 over the photosensitive elements 131 the sensor layer 13 can be applied, as these can be produced quickly, flexibly and inexpensively. Organic materials are primarily used for this in printing processes.

The photosensitive elements 131 the sensor layer 13 in a further embodiment have an electronic control unit for controlling the exposure time (not shown), for example as a rolling shutter or as a global shutter, as described in the US 2017/0085813 A1 is disclosed. This enables the exposure time and thus the integration time of the photosensitive elements 131 the different brightness of the display 17th and can be adapted by ambient light, which varies in the application scenario of the device according to the invention by the user or by different ambient light conditions. The display has to be controlled by this electronic shutter control 17th while taking skin prints 21 not necessarily be switched off and the inclusion of higher contrast skin prints 21 is still possible.

3a shows an embodiment of the laminate 1 in the side view with an enlarged view of the light guide layer 141 , with several light coupling structures as an example 144 at the bottom of the light guide layer 141 with a tilt angle ε are drawn. Is this true in the light guide layer 141 under the light guide angle α led light onto a light decoupling structure 144 with the angle of inclination ε , there is a reflection angle ϕ to the perpendicular of the light decoupling structure 144 , where: ϕ = α - ε . That at the light decoupling structure 144 reflected beam can no longer on the second adhesive layer due to its change in angle 16 are totally reflected, but passes through them and the sensor layer above them 13 , the first layer of adhesion 15 and the top layer 12th . Depending on the refractive index of the top layer 12th indicates this to the contact surface 11 hitting illuminating light an illuminating angle β on that on the bearing surface 11 (Interface with air) the illuminating light is totally reflected and a picture of skin prints 21 (not shown) according to the principle of disturbed total internal reflection (FTIR or short: TIR).

3b shows a further embodiment of the laminate 1 in the side view with an enlarged view of the light guide layer 141 , in this example several light coupling structures 144 at the top of the light guide layer 141 available. The light decoupling structures 144 are designed so that in the light guide layer 141 guided light when hitting the light decoupling structures 144 a first time at the interface with the second adhesive layer above 16 and a second time at the interface with the sensor layer 13 at a defined angle of refraction γ from the light guide layer 141 towards the top layer 12th uncouples. Here, the main beam is in the light guide layer 141 led light with the angle α including a divergence when hitting the light decoupling structure 144 decoupled, with no further restriction of the divergence by the angle of inclination ε (not shown) of the light decoupling structures 144 he follows. Although this makes the light decoupling more efficient in terms of light intensity, the vertical divergence of the decoupled beam is greater than in the case of 3a , which can result in reduced resolution. The maximum possible change in the angle is also between α and β lower than at 3a .

The type and shape of the light decoupling structures 144 in the material of the light guide layer 141 are two examples of the shape and distribution for a section of the light guide layer 141 in 3c as top views to illustrate the light decoupling structure 3a and 3b drawn. In addition to the shapes of rectangles and trapezoids shown, triangles, circular sectors or circular sections or sections of ellipses are also suitable.

4a and 4b show the relationships for the embodiment in 3a between the light guide angle α , the lighting angle β , the reflection angle ϕ, the exit angle δ and the angle of inclination ε . Depending on the differences in the refractive indices between the light guide layer 141 and the adjacent adhesive layers 16 and 18th preferred angles are defined (exit angle δ ), under which illuminating light from the light guide layer 141 is decoupled. This is in 4a in the side view a schematic beam path for light decoupling structures 144 at the bottom of the light guide layer 141 outlined, the light guide layer 141 for example a refractive index of n = 1.49 and the adjacent adhesive layers 16 and 18th have a refractive index of n = 1.41.

1. I: Geführte Strahlen (a > 71°) müssen an Lichtauskoppelstruktur 144 totalreflektiert werden $$\varphi >{\text{sin}}^{-1}\frac{1.41}{1.49}=71°\text{I}\varphi =\alpha -\epsilon$$
   
2. II: Der durch die Lichtauskoppelstruktur 144 abgelenkte Strahl, der mit dem Austrittswinkel δ = α - 2·ε an der Oberseite der Lichtleiterschicht 141 auftrifft, darf dort nicht totalreflektiert werden $$\delta <{\text{sin}}^{-1}\frac{1.41}{1.49}<71°$$
   
3. III: Am Deckschicht-Luft-Übergang muss Totalreflexion stattfinden (Deckschicht 12 mit n = 1,49 angenommen) $$\delta >{\text{sin}}^{-1}\frac{1.00}{1.49}=42°$$
   

Also includes 4b the three conditions (identified by Roman numerals I. , II , III ) that must be met to ensure that the device works properly:

1. I: Guided beams (a> 71 °) must be at the light decoupling structure 144 be totally reflected $$\varphi >{\text{sin}}^{-1}\frac{1.41}{1.49}=71°\text{I.}\varphi =\alpha -\epsilon$$
   
2. II: The one through the light decoupling structure 144 deflected beam that with the exit angle δ = α - 2 · ε on the top of the light guide layer 141 hits, must not be totally reflected there $$\delta <{\text{sin}}^{-1}\frac{1.41}{1.49}<71°$$
   
3. III: Total reflection must take place at the top layer-air transition (top layer 12th with n = 1.49 assumed) $$\delta >{\text{sin}}^{-1}\frac{1.00}{1.49}=42°$$
   

The graphic in 4b shows the permitted combinations of the light guiding angle for the above numerical example α of that in the light guide layer 141 led light and tilt angle ε the light decoupling structures 144 , for imaging according to the invention when taking a skin impression 21 contribute (I + II + III). For an angle of inclination ε the light decoupling structures 144 of ε ~ 10 most of the rays are coupled out, which originally had a light guiding angle of α = 85 ° +/- 5 °. For the sensor layer 13 and top layer 12th with a similar refractive index as the light guide layer 141 (n ~ 1.5), this results in an angle spectrum β ∼ δ = 65 ° +/- 5 °. The uniform coupling of light over the entire surface of the light guide layer 141 and thus a homogeneous illumination of one on the contact surface 11 overlying skin print 21 , by adjusting a fill factor of the light decoupling structures 144 implemented.

In the embodiment with light decoupling structures, as in 3a drawn, the vertical divergence of the decoupled illuminating light compared to the embodiment in 3b very exactly about the angle of inclination ε the light decoupling structures 144 and the difference in refractive indices between the light guide layer 141 and the adjacent adhesive layers 16 , 18th can be set. Depending on the application, the device according to the invention can do more in the direction of light intensity or a narrow angle spectrum of the illuminating light can be optimized. High quality skin prints 21 With high resolution you get that from the light guide layer 141 outcoupled light has a very low divergence, so the outcoupled angle spectrum is small.

To reduce the influence of stray light 4th , caused primarily by ambient light, is in a preferred embodiment, which in 5 is shown between the top layer 12th and sensor layer 13 a first layer of adhesion 15 used, which has a refractive index which is as large as the refractive index of the second adhesive layer 16 between sensor layer 13 and light guide layer 141 . Ambient light while taking skin prints 21 ensures that the skin of the finger 2nd lights up and over the mountains of light into the top layer 12th couples. This happens due to multiple scattering in the skin and thus parts of the ambient light couple over those on the contact surface 11 positioned skin area in the top layer 11 on. This stray light 4th worsens the absorption of skin prints 21 because the stray light 4th reduces the contrast in the final image. A portion of the stray light 4th therefore does not reach the sensor layer 13 , because portions of the stray light 4th within the top layer 12th the conditions of total reflection at the interface between the cover layer 12th and first adhesive layer 15 fulfill.

Comes as a top layer 12th for example glass (n ~ 1.5) and a first adhesive layer 15 with a refractive index of 1.4 is used, then stray light 4th with angles greater than 70 ° orthogonal to the contact surface 11 at the interface of the top layer 12th and first adhesive layer 15 totally reflected and does not reach the sensor layer 13 . Thus, parts of the stray light 4th from the photosensitive sensor elements 131 not detected and the contrast of the skin prints 21 will be improved. In a particularly preferred embodiment comes for the top layer 12th a material with a larger refractive index is used. Flint glass or sapphire, for example, have a refractive index of n> 1.7, which means that even more stray light components within the cover layer 12th be totally reflected and not to the sensor layer 13 reach. With a refractive index of n = 1.7, all stray light components are totally reflected at an angle greater than 56 °. The greater the difference in refractive indices between the top layer 12th and first adhesive layer 15 is, the more stray light 4th is inside the top layer 12th totally reflected and not from the photosensitive elements 131 the sensor layer 13 detected.

6 shows a further expedient embodiment of the device according to the invention, which differs from 2nd two adjacent light guide layers 141 , 141 ' having. The further light guide layer 141 ' brings several advantages.

Due to the high transparency of light guides, several light guide layers can be used 141 , 141 ' arranged arbitrarily one above the other and connected to each other by another lower refractive adhesive. Such an additional adhesive layer 18th should have the same refractive index as the second adhesive layer 16 between the light guide layer 141 and the sensor layer 13 . First, there are various options, such as the light guide layers 141 and 141 ' be fed with light. First there is the in 6 drawn variant, in which the light guide layers 141 , 141 ' from the same narrow side of the laminate 1 with LEDs 142 are provided. The first advantage for this is an increase in the intensity of the outcoupled light, since both light guide layers 141 are highly transparent and the further light guide layer 141 ' the first light guide layer 141 in fact not perceiving. This results in the advantage of protection against ambient light, since an increase in the TIR illumination intensity (which can thus be “adjusted”) and, at the same time, a reduction in the exposure time (reduction in the exposure times of one in the sensor layer) 13 implemented electronic shutters when there is a lot of ambient light) shifts the lighting ratio in the direction of the TIR lighting intensity, which relatively reduces the influence of ambient light and thus enables a higher-contrast recording of skin prints.

In addition, the light rays that are coupled out parallel to one another are offset from one another when viewed from the top view and contribute to the homogenization of the lighting by each light guide layer 141 only a certain part of the contact surface 11 illuminated, which means that very large contact surfaces 11 for example, for the recording of entire palms, or several hands can be illuminated.

The second advantage is that multiple exposures with only one illumination of the same type of light guide layers 141 , 141 ' etc. made one after the other, the pictures can be compared and the better one can be selected. This is in addition to live detection measures for the absorption of dry and damp skin prints 21 Interesting. In the further light guide layer for living detection 141 ' Illuminating light with other wavelengths (e.g. UV , IR ) can be used in addition to VIS spectral ranges.

A third advantage arises when the two light guide layers 141 different angles of inclination ε their light decoupling structures 144 have and the further light guide layer 141 ' for example, causes an illumination angle β 'that is not suitable for TIR, but rather directly through the contact surface 11 the top layer 12th comes out and there is an open document 3rd can illuminate. The first light guide layer can be used for this document reading mode 141 can also be switched off so that no TIR light is generated. This will result in a higher-contrast recording of documents 3rd enables because the internally totally reflected illumination light of the light guide layer 141 does not interfere with the recording if it can be switched off.

In a modified variant of 6 can the light of the leds 142 for each of the light guide layers 141 and 141 ' on different, preferably opposite, narrow sides of the laminate 1 be initiated. This variant is shown by the dashed LED 146 on the right narrow side of the light guide layer 141 ' This selectable alternative is shown symbolically and illustrates.

In this alternative case, they lead out of the light guide layers 141 and 141 ' decoupled beams to two different images with an offset that can be calculated out, and thus the two fingerprint images are compared with one another for the purpose of quality improvement and the better image is selected or both images are fused with one another via subsequent image processing.

7 shows a further modified version of 2nd , which is characterized in that between the sensor layer 13 and the light guide layer 141 an additional substrate 172 is inserted, which is advantageous both for reasons of stability and for lighting homogenization.

Furthermore, in 7 over the sensor layer 13 one - here as an example as a full-surface spectral filter layer 19th drawn - filter layer inserted, which above all can make an additional elimination of the ambient light.

The spectral filter layer 19th can preferably be structured only over the photosensitive elements 131 the sensor layer 13 be applied, whereby the light of a light-emitting display applied below the device 17th from the spectral filter layer 19th remains unaffected. The spectral filter layer 19th is in a preferred embodiment a narrow band filter and on the wavelength of the illuminating light of the light guide layer 141 adjusted so that it is transparent to most parts of the illuminating light and absorbs the rest of the light.

How from 7 can also be seen, is due to the greater layer thickness between the light guide layer 141 and contact surface 11 the top layer 12th a stronger bundle broadening of the illumination beams can be observed. This is due to two at the bottom of the light guide layer 141 decoupled beams shown because of the additional substrate 172 already on the contact surface 11 the top layer 12th overlap.

In this invention, the signal broadening or widening of the beam is closely related to a fill factor of the light decoupling structures 144 the light guide layer 141 . For example, the fill factor is 1% and each light decoupling structure 144 is approx. 10 µm long (or has a diameter of 10 µm), the average length to the nearest light decoupling structure 144 around 1 mm. The signal broadening depends on the divergence (FWHM e.g. 10 ° or ± 5 ° around the illumination angle β ) and the distance between the light decoupling elements 144 and the contact surface 11 (eg 5.5 mm) and in this example results in a signal broadening of a decoupled light point to approximately 8.5 mm. This means that the maximum distance between the light decoupling structures 144 should not exceed approx. 4 mm in this example. As shown above, however, the distance is only approx. 1 mm, which means that every point of the contact surface 11 of several light decoupling elements 144 is illuminated and the sensor layer 13 the individual discrete-emitting light points of the light decoupling structures 144 the light guide layer 141 does not "see".

For uniform illumination of the contact surface 11 without intensity peaks due to individual light decoupling structures 144 two variants are available.

On the one hand, it is possible for the light decoupling structures 144 have a distance s (not shown) which is much smaller than their signal broadening up to the contact surface 11 , because then the beams of the individual light coupling structures overlap 144 before going to the support surface 11 the top layer 12th or towards the sensor layer 13 reflect. On the other hand, in a second variant it is possible for the light decoupling structures 144 have a distance s which is very much smaller than the center distance of the photosensitive elements, since in this case the signal broadening of the beams is not absolutely necessary.

Another preferred embodiment without a display 17th is in 8th shown. Here is the light guide layer 141 under the sensor layer 13 designed so that the lighting angle is proportional β to illuminate a skin print 2nd and illuminating light with the illuminating angle β 'for Illumination of documents 3rd from the light guide layer 141 towards the contact surface 11 be coupled out. The proportions of light used to illuminate documents 3rd (Illumination angle β ' ) couple from the top layer 12th towards the air, illuminate the document 3rd and that from the document on top 3rd backscattered light is emitted by the sensor layer 13 detected. Because between the document on top 3rd and the contact surface 11 there is no optical coupling, but there is always a thin layer of air, the document can 3rd not in the top layer 12th internally totally reflected light with the illumination angle β be illuminated.

The device according to the invention includes a display 17th , the display will 17th emitted light as illuminating light for holding documents 3rd used as this comes from the top layer 12th decouples in the direction of air and an adaptation of the light decoupling structures 144 the light guide layer 141 is not required. If the device, as in 8th shown, operated, the angle of illumination β ' for illuminating overlay documents 3rd can also be visually perceived by the user of the device when light is used in the visual range of the light spectrum. The glow of the contact surface 11 Can be identified as simplified user guidance when the device is ready to take skin prints 21 or documents 3rd is without a display 17th is required. The proportion of illuminating light that passes over the top layer 12th coupled out to the air, should preferably be relatively small compared to the totally reflecting illuminating light and should be less than 50%, since this proportion of light when recording skin prints 21 acts as contrast light to reduce contrast. In a preferred embodiment, the light decoupling structures are 144 formed so that between 50% and 95% of that from the light guide layer 141 decoupled illuminating light at the transition to air on the contact surface 11 in the top layer 12th are totally reflected light and can be used to illuminate skin (angle of illumination β ), while a remaining portion of light illuminates the illumination angle for illuminating documents 3rd is usable (lighting angle β ' ).

Is the vertical divergence around the light guide angle α of that in the light guide layer 141 led light large enough, lighting angles are automatically β , β ' for illuminating skin prints 21 (Illumination angle β ) and documents 3rd (Illumination angle) towards the top layer 12th uncoupled. Is the top layer 12th made of a material with a refractive index of - 1.5 (e.g. glass) and lies the angle of illumination β at 50 ° and has a divergence of +/- 10 °, lighting angles will be β ' decoupled between 40 ° and 42 ° in air and for illuminating an overlay document 3rd used.

This procedure can also be shown in the 8th due to different inclination angles ε the light decoupling structures 144 will be realized. Different angles of inclination ε and ε 'provide different reflection angles ϕ and ϕ' on the corresponding light decoupling structures 144 and lead to different lighting angles β and β ' on the contact surface 11 . This allows the proportions of the illuminating light for skin prints 21 and documents 3rd can be controlled directly. In 8th are examples in the enlarged detail view of the light decoupling structures 144 two different angles of inclination ε and ε ' shown, so that the reflection angles ϕ and ϕ 'of the light decoupling structures 144 and thus the lighting angle β and β ' vary, ie both lighting conditions for skin prints 21 and for documents 3rd from the same light guide layer 141 can be generated. The different light decoupling structures 144 can be in independent grids (not shown). In a preferred embodiment, every tenth light coupling structure is for this 144 with an angle of inclination ε ' trained of an illumination angle β ' for illuminating documents 3rd realized so that 90% of the decoupled beams with the illumination angle β on the contact surface 11 in the transition to air totally reflected and to lighting for the absorption of skin prints 21 be used.

In a further embodiment there is a first area of the support surface 11 only for taking documents 3rd provided and is provided with lighting angles β ' from the light guide layer 141 illuminated and a second area of the support surface 11 is only for taking a skin print 2nd provided and is provided with lighting angles β from the light guide layer 141 illuminated, the illuminating light at the interface between the top layer 12th and air totally reflected.

Different objects, e.g. B. skin, documents etc, by choosing the design of the light decoupling elements 144 the light guide layer 141 be included. This also makes it possible to adapt the structures to the different reflection and scattering behavior of individual objects.

In 9 are different types for the coupling of illuminating light on a narrow side of the light guide layer 141 by means of several LEDs 142 and their more or less divergent emitted beams are shown in five top views, which differ in their state of pre-collimation. For these versions, it is assumed that most LEDs 142 are already internally precollimated to different degrees.

In part (a) of 9 are the coupling of illuminating light on a narrow side of the light guide layer in this regard 141 by means of several LEDs 142 and their clearly divergent beams are shown in plan view.

Various embodiments can be used as the source for the illuminating light. Be multiple LED without collimation of the beam 147 used, the individual beams overlap 147 and cause an illuminated object point to be on the support surface 11 resting finger 2nd due to different beams 147 is illuminated and on several pixels of the scanned image recording (distributed), or on several points of the sensor layer 13 (not shown here). The possible mapping of an object point to several pixels is shown in partial illustration (a) of 9 represented by the arrowheads.

By mixing the beams 147 of the several light-emitting LEDs 142 , it inevitably happens that from an object point on the support surface 11 several pixels in the sensor layer 13 are generated, with which the same object information, for example of an overlying finger 2nd on several photosensitive elements 131 is detected and the resolution of the imaged skin impression 21 decreases. The smaller the horizontal and vertical divergence of the rays 147 the higher the resolution.

In 9 shows the partial image (a) schematically in a top view of how an object point (each drawn as a black point along the lower dashed line) is mapped onto two pixels that are spaced apart (as points along the second dashed line). This happens because of the top layer 12th a distance between the contact surface 11 and sensor layer 13 exists. The smaller this distance, the less the object information runs and the better the resolution. Thicknesses from 50 µm to 1000 µm of the top layer 12th are quite common. A large thickness of the top layer 12th ensures improved mechanical protection for the device and is therefore preferred. The lower the divergence of the beam 147 is, the better the resolution or the greater the thickness of the cover layer 12th can be selected with the same resolution. An approach to improve the resolution or increase the thickness of the cover layer 12th are therefore a means of collimating the rays 147 of the LEDs 142 , as shown in other parts of 9 are shown.

In part (b) the LEDs are precollimated by the manufacturer 142 used and - as described above - packed tightly to each other and with the smallest distance to the narrow side of the light guide layer to be coupled 141 arranged. This allows you to do this without additional pre-collimation optics 143 an acceptable divergence of the rays 147 with good mixing of the light components of the individual LEDs 142 will be realized. It also happens at the interface between air and light guide layer 141 when the illuminating light is coupled in for refraction, whereby a certain pre-collimation is achieved.

If this type of coupling does not meet the requirements for the local resolution of the image recording, the design variants have an additional pre-collimation lens 143 according to the parts (c) and (d) of 9 to be preferred, in partial illustration (c) on the narrow side of the light guide layer 141 molded refractive convex lenses as pre-collimation optics 143 are selected, which can also be replaced by GRIN lenses. The refractive pre-collimation optics are shown in part (d) 143 as concave lenses in the material of the light guide layer 141 incorporated and made of an optically thinner medium, ie with a significantly lower refractive index compared to the light guide layer 141 educated. A gaseous medium, such as air, is best suited for this. The collimation state that can be achieved with exemplary embodiments according to partial illustrations (c) and (d) ensures the best possible resolution, but has the disadvantage of an uneven intensity distribution of the illumination of the contact surface 11 , so that between these two versions and the variant according to partial illustration (b) it is necessary to consider which requirements should be given priority.

In the partial illustration (e) of 9 are the tightly packed LEDs 142 equipped with different spectral radiation wavelengths, which alternate along the narrow side of the light guide layer 141 are arranged and switchable, at least two different spectral ranges being selected in order to use them to alternatively illuminate images of the objects placed on them, skin prints 2nd or documents 3rd to record, which are preferably used for proof of authenticity.

10th shows an embodiment with a light coupling on a narrow side of the light guide layer 141 and pre-collimation optics 143 in the top view.

Before the illuminating light of the multiple LEDs 142 one on the support surface 11 resting object (finger 2nd or document 3rd ) illuminated, it is advantageous that the beam 147 of the several LEDs 142 are sufficiently mixed to the contact surface 11 to illuminate evenly. In a preferred embodiment, this is due to the contact surface 1 upstream coupling areas for the beams 147 realized. For this, according to 10th for light coupling several with a minimal center distance A LED lined up closely 142 with divergent beams 147 on a narrow side of the light guide layer 141 arranged. The different beams 147 with the help of pre-collimation optics 143 pre-collimated with the aim of reducing their divergence.

As described at the beginning, the LED is precollimated 142 helpful for a good resolution of the skin print 21 to realize.

Homogeneous lighting is achieved by using pre-collimated LEDs 142 are packed as close together as possible and, as in 10th shown, a first coupling length B or even a second launch length C. for sufficient mixing to have light intensity peaks and the associated local overexposure of skin prints 21 to avoid.

As a result, the coupled adjacent divergent beams bundle overlap, particularly in the horizontal direction 147 only after the first coupling length B at the points marked with a circle. As a result, in the subsequent area of the light guide layer 141 a better distribution of light. After the second coupling length C, the beams overlap 147 the second neighbor of the LEDs 142 , whereby an almost perfect homogenization of the lighting is realized.

The lower the divergence of the LEDs 142 the better the resolution of the skin print 21 , because local object information is displayed on fewer pixels (distributed and mixed). Are the beams 147 however, the contact surface becomes too restricted (collimated) 11 unevenly or in extreme cases not illuminated at all. In this case the coupling length is sufficiently large B or B + C necessary, which depends on the center distance A two adjacent LEDs 142 and their degree of pre-collimation. Usually there is a coupling length B or B + C of a few millimeters, preferably between 2 mm and 20 mm, sufficient to ensure sufficient overlap and mixing of the radiation beams 147 to realize.

With a divergence of 10 ° and a distance of 10 mm as the center distance A of the LEDs 142 , a coupling length B of 57 mm is required so that the emitted beams of the neighboring LED overlap (tan 85 ° = A / 5). In order to meet higher homogeneity requirements, the half-widths (FWHM) of the next but one LEDs should be 142 also overlay before light on an overlying skin print 21 falls. The coupling length would have to be 114 mm (tan 85 ° = A / 10). This also shows that the LEDs 142 are preferably arranged as close as possible, ie that the center distance A of the LED 142 is as small as possible, especially when using the pre-collimation optics 143 the light cone is severely restricted, ie the FWHM is small.

In 11 three top views of further embodiment details of the device according to the invention with a so-called corner light coupling with at least one LED are shown.

11 contains a partial illustration (a), which shows an embodiment of the light coupling from an LED 142 into the light guide layer 141 shows in the top view, in which the light coupling by an LED 142 at least one by shortening a corner of the light guide layer 141 is implemented. Through a shortened corner 145 becomes an additional, very short narrow side of the light guide layer 141 generates an angle of 135 ° with the usually existing narrow sides of a rectangular light guide layer 141 having. The advantage of this embodiment is that there is no collimation of the beam 147 the LED 142 in the horizontal direction by pre-collimation optics 143 (as in 9 , Figures (c) and (d) shown) is necessary. The LED 142 should preferably be at an angle of +/- 45 ° to the adjacent rectangular narrow edges in the light guide layer 141 radiate. Each object point generates only a discrete image point in the horizontal direction, as can be seen in the partial illustration (a) using the black dots, because there is no superimposition of different beams (as opposed to 9 , Figure (a) explained). A reduction in resolution only takes place due to the vertical divergence (not shown), which, however, as already described above, is due to the slight differences in the refractive indices between the light guide layer 141 and adjacent adhesive layers 16 and 18th as well as the angle of inclination ε the light decoupling structures 144 can be severely restricted and even divergences of less than +/- 5 ° can be implemented. The drop in intensity of the in the light guide layer 141 coupled divergent beam 147 can be achieved through a growing fill factor of the light decoupling structures 144 (from size and density of the light decoupling structures 144 ) compensate towards the edge. The shape, size and density distribution of the light decoupling structures 144 can, as in 3c shown, implemented and preferably designed as a trapezoidal, desk-like rising surface elements.

With corner lighting designed in this way, reflections can occur at the edge regions of the adjacent narrow sides of the light guide layer 141 be disadvantageous, since this creates double images and lead to a deterioration in the resolution. A preferred embodiment is therefore that the light guide layer 141 on the other narrow sides, on which no light is coupled in, have absorbent coatings which absorb or couple out light incident there.

In parts (b) and (c) of 11 additional measures have been drawn compared to part (a). In part (b) there is a multiple arrangement of LEDs 142 shown, the light distribution or homogenization of the two LEDs present in this example 142 through a lens 146 is improved, through which light is emitted evenly (diffusely) in all directions. Partial illustration (c) shows a design example for the shortened corner 145 , which is designed as a concave arc, so that all divergent from the LED 142 emerging rays unbroken into the light guide layer 141 can occur, causing in the entire light guide layer 141 Propagate light source light equally distributed and can be coupled out.

With the embodiments of the invention described here are high-resolution and high-contrast images of skin prints 21 as well as documents that are based on a targeted coupling of light from a light guide layer 141 based on defined angles for internal total reflection (TIR) or for light emission for document illumination. Furthermore, aperture structures are used as an aperture layer 133 in the sensor layer 13 the individual sensor elements 131 assigned that defines only those from the light guide layer 141 Allow decoupled TIR angular ranges for detection. Additional measures of the sensor control for setting electronic shutter functions (rolling or global shutter) are further optimizations of the image recordings of skin prints 21 and security-relevant documents 3rd reachable.

Reference list

1

Laminate

11

Contact surface

12th

Top layer

13

Sensor layer

131

photosensitive elements

132

transparent areas

14

Light source unit

141

Light guide layer

141 '

(further) light guide layer

142

LED

143

Pre-collimation optics

144

Light decoupling structure

145

shortened corner

146

Lens

147

Bundle of rays

15

first adhesive layer

16

second adhesive layer

17th

Display

171

Finishing shift

172

Substrate

173

Luminous element layer

18th

additional adhesive layer

19th

Spectral filter layer (bandpass)

2nd

finger

21

Skin impression (to be recorded)

3rd

document

4th

Stray light

α

Light guiding angle (of the light guided in the light guiding layer)

β, β '

Illumination angle (on the contact surface)

δ

Exit angle (from the light guide layer

ε, ε '

Angle of inclination (of the light decoupling structure)

ϕ, ϕ '

Reflection angle (of the light decoupling structure)

γ

Angle of refraction (of the light decoupling structure)

QUOTES INCLUDE IN THE DESCRIPTION

This list of documents listed by the applicant has been generated automatically and is only included for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent literature cited

• DE 102015115484 B3 [0009]
• US 2018/0121701 A1 [0011]
• WO 2017/118030 A1 [0011]
• US 2018/0165497 A1 [0012]
• US 2018/0128957 A1 [0013]
• US 2017/0085813 A1 [0044]

Claims (17)

Device for the optical direct recording of skin impressions, with a laminated body (1), which contains a contact surface (11), which is formed by a cover layer (12) of the laminated body (1), as well as a sensor layer (13) and a light source unit (14), wherein the sensor layer (13) has photosensitive elements (131) and transparent areas (132) arranged in a sensor grid, characterized in that - the light source unit (14) is designed as a light guide layer (141) and is arranged below the sensor layer (13), wherein the light guide layer (141) has a light coupling by means of LED (142) on a narrow side, - the light guide layer (141) is provided with light decoupling structures (144) based on an angle of inclination of the light decoupling structures (144) and on differences in the refractive indices between the neighboring layers of the Light guide layer (141) up to the cover layer (12) a directional light coupling out of the light guide layer t (141) at a defined angle, which after passing through all layers up to the top layer (12) on the support surface (11) leads to total internal reflection (TIR) at the transition to air, and with a small divergence angle range of ≤ +/- 15 ° allow a high local resolution of the skin impression (21) to be recorded, - between the cover layer (12) and the sensor layer (13) a first adhesion layer (15) and between the sensor layer (13) and the light guide layer (141) a second adhesion layer (16) are present, wherein - the second adhesion layer (16) has a refractive index which is at least 1% and at most 30% smaller than the refractive indices of the light guide layer (141) and the sensor layer (13), the refractive indices of which are between 1.45 and 1.8 lie, and - the first adhesive layer (15) has a refractive index which is at least as large as that of the second adhesive layer (16). Device after Claim 1 , characterized in that the LED light coupling has a precollimation optics (143) downstream of the LED (142) on the narrow side of the light guide layer (141), with which a horizontal divergence between 2.5 in the beam bundle coupled into the light guide layer (141) ° and 30 ° is set in order to achieve an improved resolution of the skin impression (21) to be recorded. Device after Claim 2 , characterized in that the pre-collimation optics (143) is a refractive optical element which is incorporated on the narrow side of the light guide layer (141). Device after Claim 3 , characterized in that the pre-collimation optics (143) are incorporated in the form of a convex or GRIN lens on the narrow side of the light guide layer (141). Device after Claim 3 , characterized in that the pre-collimation optics (143) within the light guide layer (141) is designed in the form of a concave lens made of a medium with a lower refractive index than the light guide layer (141). Device according to one of the Claims 2 to 5 , characterized in that a plurality of closely adjacent LEDs (142) are arranged along a narrow side of the light guide layer (141), so that their beam bundles have an adjusted light intensity in the light guide layer (141) due to the horizontal divergence after a defined coupling-in length (B, C) cause. Device after Claim 1 , characterized in that a corner light coupling with at least one LED (142) is arranged on at least one narrow side provided by shortening a corner of the light guide layer, an intensity drop in the divergent beam bundle coupled into the light guide layer (141) due to a growing fill factor of size and density of the Light decoupling structures (144) is compensated. Device after Claim 7 , characterized in that a diffusing screen is arranged between the LED and the narrow side of the shortened corner (145) of the light guide layer (141) for uniform distribution of the coupled light in all solid angles, so that there is no light drop at the narrowed corner (145) adjacent narrow sides of the light guide layer (141) is to be compensated. Device after Claim 1 , characterized in that the refractive index of the first adhesive layer (15) is the same size as the refractive index of the second adhesive layer (16), so that a proportion of stray light (4) resulting from excitation generated by ambient light from those on the contact surface (11) overlying skin areas (21), due to TIR within the cover layer (12) from being spread out in the direction of the sensor layer (13). Device after Claim 1 , characterized in that the laminate (1) has a display (17) for displaying user information, which is placed below the light guide (141). Device after Claim 10 , characterized in that the display (17) on the underside of the light guide layer (141) either removable without an adhesive layer or by means of a further low-index adhesive layer (18) with a Refractive index, which is at most as large as that of the second adhesive layer (16) is attached. Device according to one of the Claims 1 to 11 , characterized in that the light outcoupling structures are designed such that only between 50% and 95% of the illuminating light outcoupled from the light guide layer (141) are totally reflected light portion during the transition to air on the contact surface (11) in the cover layer (12), while remaining light portion can be used to illuminate documents (3). Device according to one of the Claims 1 to 12th , characterized in that the fill factor of the light decoupling structures (144), formed by the size and spacing of the light decoupling structures (144), is at least so great for each point of the light guide layer (141) that the light decoupling structures (144) are not in an imprint image of skin areas are visible. Device after Claim 13 , characterized in that the light outcoupling structures (144) have a distance s which is very much smaller than a resulting beam divergence of the light outcoupling structures (144) of the light guide layer (141). Device according to one of the Claims 1 to 14 , characterized in that a further transparent light guide layer (141 ') is attached under the transparent light guide layer (141) and is connected to this by a further adhesion layer (18) which has a low refractive index like the first and second adhesion layer (16). Device after Claim 15 , characterized in that the light guide layer (141) and the further light guide layer (141 ') have the light coupling on opposite narrow sides of the layer body (1). Device after Claim 15 , characterized in that the light guide layer (141) and the further light guide layer (141 ') have the light coupling on the same narrow side of the layer body (1) and have light coupling structures (144) with the same orientation, the light guide layer (141) and the further light guide layer ( 141 ') can have light decoupling structures (144) with such different angles of inclination ε, insofar as these different angles of inclination ε each produce illumination angles β which lead to total reflection on the contact surface (11).

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